Tuning Solvation Structures with KPF₆ Additives for More Stable Lithium Metal Battery Cycling

Abstract

Uncontrolled dendrite growth and low Coulombic efficiency remain major challenges limiting the practical application of rechargeable lithium metal batteries. Here, we introduce potassium hexafluorophosphate (KPF₆) as an additive to a commercial 1 m LiPF₆-EC/DEC (1:1 vol%) electrolyte, which induces the formation of positively charged small aggregates in which a PF₆⁻ anion is shared between Li⁺ and K⁺ solvation structures. Molecular dynamics simulations reveal that the 0.1 m KPF₆-containing electrolyte exhibits a higher Li⁺ diffusion coefficient than in the baseline system, consistent with its enhanced ionic conductivity and transference numbers. Complementary density functional theory calculations show that these small aggregates possess lower solvation energies, facilitating Li⁺ desolvation, while their reduced LUMO energy promotes LiPF₆ decomposition to generate a robust inorganic-rich SEI. Experimentally, the KPF₆ additive drives the formation of a smooth, uniform, and ion-conductive SEI on lithium metal, enabling Li‖LiFePO₄ cells to deliver superior rate capability and capacity retention. Pouch cell tests further underscore the practical potential of this electrolyte design. These findings highlight the role of small aggregates in solvation structure engineering and provide new insights for the development of high-performance lithium metal batteries.

Keywords

enhanced stability and performance / KPF₆ electrolyte additive / Lithium metal battery / small aggregates

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